[user104658]

Murder, because of what Alex said above. Murders are either carried out by people who are mentally unhinged, or are crimes of passion where anger has overwhelmed someone and they've snapped. It's not murder being "illegal" that stops people from killing each other... A normal person on a normal day just has no compulsion to kill. It's not really "in us". You can see this in the trauma that many soldiers etc. face after making their first (completely "legal") kill... It has a profound effect even then.

Of course you could then say, with it being legal there would be murderers roaming the street because they wouldn't be locked up. But there's a convenient loophole there. If murder is legal, then vigilante justice / revenge killings are legal. So if there's some psychopathic killer roaming about, the friends and family of those killed can hunt him down and tear him to pieces. It's legal!